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Natural-gas operations in areas such as Wyoming’s Jonah Field could release far more methane into the atmosphere than previously thought.
C LIM ATE CHANGE
Air sampling reveals high
emissions from gas field
Methane leaks during production may offset climate benefits of natural gas.
BY JEFF TOLLEFSON
W
hen US government scientists
began sampling the air from a
tower north of Denver, Colorado,
they expected urban smog — but not strong
whiffs of what looked like natural gas. They
eventually linked the mysterious pollution to a nearby natural-gas field, and their
investigation has now produced the first hard
evidence that the cleanest-burning fossil fuel
might not be much better than coal when it
comes to climate change.
Led by researchers at the National Oceanic
and Atmospheric Administration (NOAA)
and the University of Colorado, Boulder, the
study estimates that natural-gas producers in
an area known as the Denver-Julesburg Basin
are losing about 4% of their gas to the atmosphere — not including additional losses in
the pipeline and distribution system. This is
more than double the official inventory, but
roughly in line with estimates made in 2011
that have been challenged by industry. And
because methane is some 25 times more efficient than carbon dioxide at trapping heat in
the atmosphere, releases of that magnitude
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© 2012 Macmillan Publishers Limited. All rights reserved
A LOSING BATTLE
Estimates of methane losses from gas fields near Denver, Colorado, based on air
sampling differ considerably from calculations based on industry activity.
Inventory
of industry
activity
Range of
uncertainty
Monitoring
tower
Mobile lab
0
50
100
150
200
Billion grams of methane per year
could effectively offset the environmental
edge that natural gas is said to enjoy over other
fossil fuels.
“If we want natural gas to be the cleanest
fossil fuel source, methane emissions have to
be reduced,” says Gabrielle Pétron, an atmospheric scientist at NOAA and at the University
of Colorado in Boulder, and first author on the
study, currently in press at the Journal of Geophysical Research. Emissions will vary depending on the site, but Pétron sees no reason to
think that this particular basin is unique.
“I think we seriously need to look at naturalgas operations on the national scale.”
The results come as a natural-gas boom
hits the United States, driven by a technology
known as hydraulic fracturing, or ‘fracking’,
that can crack open hard shale formations and
release the natural gas trapped inside. Environmentalists are worried about effects such
as water pollution, but the US government is
enthusiastic about fracking. In his State of the
Union address last week, US President Barack
Obama touted natural gas as the key to boosting domestic energy production.
LACK OF DATA
Natural gas emits about half as much
carbon dioxide as coal per unit of energy
when burned, but separate teams at Cornell
University in Ithaca, New York, and at the
US Environmental Protection Agency (EPA)
concluded last year that methane emissions
from shale gas are much larger than previously thought. The industry and some
academics branded those findings as exaggerated, but the debate has been marked by
a scarcity of hard data.
“It’s great to get some actual numbers from
the field,” says Robert Howarth, a Cornell
researcher whose team raised concerns about
methane emissions from shale-gas drilling in
a pair of papers, one published in April last
year and another last month (R. W. Howarth
et al. Clim. Change Lett. 106, 679–690; 2011;
R. W. Howarth et al. Clim. Change in the
press). “I’m not looking for vindication here,
but [the NOAA] numbers are coming in very
250
300
close to ours, maybe a little higher,” he says.
Natural gas might still have an advantage
over coal when burned to create electricity,
because gas-fired power plants tend to be newer
and far more efficient than older facilities that
provide the bulk of the country’s coal-fired
generation. But only 30% of US gas is used to
produce electricity, Howarth says, with much of
the rest being used for heating, for which there
is no such advantage.
ON THE SCENT
The first clues appeared in 2007, when NOAA
researchers noticed occasional plumes
of pollutants including methane, butane
and propane in air samples taken from a
300-metre-high atmospheric monitoring
tower north of Denver. The NOAA researchers worked out the general direction that the
pollution was coming from by monitoring
winds, and in 2008,
the team took advan- “A big part of it
tage of new equipment is just raw gas
and drove around the
that is leaking
region, sampling the
from the
air in real time. Their
infrastructure.”
readings led them to
the Denver-Julesburg
Basin, where more than 20,000 oil and gas
wells have been drilled during the past four
decades.
Most of the wells in the basin are drilled
into ‘tight sand’ formations that require the
same fracking technology being used in shale
formations. This process involves injecting a
slurry of water, chemicals and sand into wells
at high pressure to fracture the rock and create
veins that can carry trapped gas to the well.
Afterwards, companies need to pump out the
fracking fluids, releasing bubbles of dissolved
gas as well as burps of early gas production.
Companies typically vent these early gases
into the atmosphere for up to a month or more
until the well hits its full
NATURE.COM
stride, at which point it is
Should fracking
hooked up to a pipeline.
stop?
The team analysed
go.nature.com/adox2r the ratios of various
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© 2012 Macmillan Publishers Limited. All rights reserved
pollutants in the air samples and then tied
that chemical fingerprint back to emissions
from gas-storage tanks built to hold liquid
petroleum gases before shipment. In doing
so, they were able to work out the local emissions that would be necessary to explain the
concentrations that they were seeing in the
atmosphere (see ‘A losing battle’). Some of
the emissions come from the storage tanks,
says Pétron, “but a big part of it is just raw
gas that is leaking from the infrastructure”.
Their range of 2.3–7.7% loss, with a best guess
of 4%, is slightly higher than Corn­ell’s estimate of 2.2–3.8% for shale-gas drilling and
production. It is also higher than calculations
by the EPA, which revised its methodology
last year and roughly doubled the official US
inventory of emissions from the natural-gas
industry over the past decade. Howarth says
the EPA methodology translates to a 2.8% loss.
The Cornell group had estimated that 1.9%
of the gas produced over the lifetime of a typical
shale-gas well escapes through fracking and well
completion alone. NOAA’s study doesn’t differentiate between gas from fracking and leaks
from any other point in the production process,
but Pétron says that fracking clearly contributes
to some of the gas her team measured.
Capturing and storing gases that are being
vented during the fracking process is feasible,
but industry says that these measures are too
costly to adopt. An EPA rule that is due out as
early as April would promote such changes by
regulating emissions from the gas fields.
Officials with America’s Natural Gas
Alliance, based in Washington DC, say that
the study is difficult to evaluate based on
a preliminary review, but in a statement to
Nature they add that “the findings raise questions and warrant a closer examination by the
scientific community”. Environmental groups
are pushing the EPA to strengthen pollution
controls in the pending rule, but industry is
pushing to relax many of the requirements.
Many companies are already improving their
practices and reducing emissions throughout
the country, either voluntarily or by regulation, the alliance says.
Not all studies support the higher methane
numbers. Sergey Paltsev, assistant director
for economic research at the Massachusetts
Institute of Technology Energy Initiative in
Cambridge, and his colleagues are gathering information about industry practices for
a study on shale-gas emissions. He says that
their figures are likely to come in well below
even the lower EPA estimate. He calls the
NOAA results “surprising” and questions how
representative the site is.
Pétron says that more studies are needed
using industry inventories and measurements
of atmospheric concentrations. “We will never
get the same numbers,” she says, “but if we can
get close enough that our ranges overlap in a
meaningful way, then we can say we understand the process.” ■
G. PÉTRON ET AL. J. GEOPHYS. RES.
NEWS IN FOCUS